Second world war spy stories sometimes give the impression that the war was fought not just half a century ago, but in another universe altogether. If modern war seems to be prosecuted by hubristic technocrats wiggling joysticks in the bowels of the Pentagon, then the key players in the second world war were moustached minor aristocrats escaping from POW camps on motorbikes, roaring across Europe in powerful cars, and concealing microfilm in strings of onions.

The title of Clare Mulley's biography, playing on Fleming, indicates that this book is in that tradition. Christine Granville was, at least apocryphally, Winston Churchill's favourite spy. Born Maria Krystyna Janina Skarbek, daughter of a charming but dissolute Polish aristocrat and a Jewish banking heiress, she was described in 1939 as "a flaming Polish patriot … expert skier and great adventuress". So she was. In Cape Town when the war began, she sailed to Southampton and presented herself to the British secret service, demanding a job. That she worked for the British would later cause her problems with her compatriots, and that she was Polish would at various times cause the British to mistrust her. But she was determined to do anything she could to help Poland against the Nazis.

There's no shortage of exploding-cigar stuff here. Microfilm gets sewn into the lining of Christine's gloves or embedded in blocks of shaving soap. The detonators for limpet mines used to blow up barges on the Danube were "concealed inside Woolworths aniseed balls whose dissolving rate had been vigorously tested in Bedford Modern School swimming pool". And how's this for the spy's toolkit:

As "Jacqueline Armand", code-name "Pauline", Christine had been issued a rubber-lined crash-helmet, loaded revolver, razor-edged commando knife, torch, and a round, brown, rubber-coated cyanide tablet sewn into the hem of her skirt. She had French papers forged near Harlow by the cream of British and Polish professionals, who happened to be out of prison when recruited, and a money-belt stuffed with gold sovereigns. In some accounts she was given a square of silk printed with a local map, a compass hidden behind her hairclip, and a magnifying glass placed in the end of a cigarette.

The verb in Mulley's title does invite you to complete the sentence, though: "not wisely but too well"? "Indiscriminately"? "Everyone with at least one leg and a pair of trousers"? Men went nuts for Christine, and she wasn't the monogamous type. She jumped into bed with practically everybody she met: but men needed her more than she needed men.

Her longest and most serious relationship was with Andrzej Kowerski – a one-legged Polish war hero who was her wing-man in Budapest, Poland and Cairo – but it didn't stop her having an affair with his friend, the two-legged Polish war hero Wladimir Ledóchowski. Not to mention bopping the odd Serbian war hero, having a tumble with her married SOE (Special Operations Executive) colleague when she parachuted into occupied France to help the Maquis, becoming a "very special friend" to a rangy Alpine mountaineer, and so on. All this, while her second husband was wandering around somewhere in the background.

When she was in Budapest, a British intelligence report noted: "Her attractiveness appeared to be causing some difficulty." Specifically, one of her suitors was threatening to shoot himself "in his genital organs" at her flat. He lost his nerve and shot himself in the foot, but as soon as he was able to walk he threw himself into the Danube, not realising it was still half-frozen. Instead of drowning he broke his remaining good leg.

Even dogs couldn't resist her. How many history books contain, and then go on to justify, the sentence "It would not be the only trained patrol dog she subverted"? The second dog, Mulley reports straight-faced, permanently switched allegiance and remained on the Allied side for the rest of the war.

Romance was one thing, but it was danger that really seemed to ring Christine's bell. She was astonishingly courageous and resourceful. She cut her teeth as a spy infiltrating Poland from Hungary over the Carpathians on skis. When forced to cool her heels in Cairo (Mulley reports the probably apocryphal story that the HQ of the SOE in Cairo was so ill-concealed that taxi-drivers all knew it as "Secret House" and street vendors outside shouted "Chocolates! Cigarettes! OBEs!"), she lobbied incessantly to be given an active role. She parachuted into occupied France. She single-handedly persuaded a whole garrison of Polish conscripts into the Wehrmacht, on a key Alpine pass, to surrender to the Allies. And she effected – again, single handedly – a breathtakingly brave 11th-hour rescue of two comrades from the Gestapo HQ where they were due to be executed. She was erroneously, but plausibly, said to have been the model for Ian Fleming's Vesper Lynd.

The backdrop to this story of ripping yarns and ripping stockings, Mulley now and again reminds us, is grindingly horrific, though. Nobody's war was much fun, but Poland's was particularly foul: betrayed by Britain, raped by Hitler, carved up by Stalin and Roosevelt. In the poignant words of one Polish radio transmission sent just after the fall of Warsaw: "Absolutely everyone has lost absolutely everything." In very quick succession we get the Katyn massacre, the clearance of the Warsaw ghetto and the death of General Sikorski. Only in the last case can there be the hint of a Boys' Own spin. Responding to conspiracy theories, a senior British spook wrote pertly to the Times: "Sir, if General Sikorski had been murdered, I would have had to do it. I didn't. Yours etc, Patrick Howarth."

There's a line of personal disgrace here, too. Britain's behaviour towards Poland during the war was shameful, and its behaviour to Christine afterwards was in the same vein. Dumped from the post-war SOE ("cannot type, has no experience whatever of office work and is altogether not a very easy person to employ"), short-changed on honours, forced to petition pathetically for British nationality against an obdurate and sexist bureaucracy, Christine was reduced to making ends meet by getting work as a telephone operator, sales assistant, linen-cupboard attendant at a hotel, and stewardess on a shipping line.

The latter job was, finally, what did for her. This amazing woman was stabbed to death in the lobby of a South Kensington hotel by a merchant seaman she'd had an affair with and then rejected. The wretched man's last words before he was hanged were: "To kill is the final possession."